#include <iostream>
using namespace std;
typedef long long ll;

ll gcd(ll n, ll m)
{
    if (m == 0)
    {
        return n;
    }
    return gcd(m, n % m);
}

ll lcm(ll n, ll m)
{
    return n / gcd(n, m) * m;
}

int main()
{
    ll n;
    int m;
    cin >> n >> m;
    ll b[100005], c[100005];
    for (int i = 0; i < m; i++)
    {
        cin >> b[i] >> c[i];
        c[i] = (c[i] % b[i] + b[i]) % b[i];
    }
    ll l = 1, x = 0;
    for (int i = 0; i < m; i++)
    {
        while (x <= n)
        {
            if (x % b[i] == c[i])
            {
                break;
            }
            x += l;
        }
        l = min(n + 1, lcm(l, b[i]));
    }
    if (x <= n)
    {
        cout << x << endl;
    }
    else
    {
        cout << "NaN" << endl;
    }
}